全文获取类型
收费全文 | 11189篇 |
免费 | 1864篇 |
国内免费 | 1185篇 |
专业分类
化学 | 6375篇 |
晶体学 | 76篇 |
力学 | 511篇 |
综合类 | 45篇 |
数学 | 1054篇 |
物理学 | 3089篇 |
无线电 | 3088篇 |
出版年
2024年 | 48篇 |
2023年 | 308篇 |
2022年 | 443篇 |
2021年 | 484篇 |
2020年 | 591篇 |
2019年 | 469篇 |
2018年 | 444篇 |
2017年 | 371篇 |
2016年 | 495篇 |
2015年 | 549篇 |
2014年 | 665篇 |
2013年 | 803篇 |
2012年 | 939篇 |
2011年 | 992篇 |
2010年 | 701篇 |
2009年 | 629篇 |
2008年 | 663篇 |
2007年 | 582篇 |
2006年 | 594篇 |
2005年 | 502篇 |
2004年 | 348篇 |
2003年 | 326篇 |
2002年 | 361篇 |
2001年 | 247篇 |
2000年 | 229篇 |
1999年 | 223篇 |
1998年 | 167篇 |
1997年 | 160篇 |
1996年 | 177篇 |
1995年 | 139篇 |
1994年 | 122篇 |
1993年 | 83篇 |
1992年 | 83篇 |
1991年 | 69篇 |
1990年 | 48篇 |
1989年 | 42篇 |
1988年 | 40篇 |
1987年 | 20篇 |
1986年 | 27篇 |
1985年 | 21篇 |
1984年 | 12篇 |
1983年 | 5篇 |
1982年 | 1篇 |
1981年 | 6篇 |
1980年 | 1篇 |
1957年 | 3篇 |
1935年 | 1篇 |
1931年 | 1篇 |
1930年 | 3篇 |
1922年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
有线电视电缆网采用供电器进行集中供电,要计算一个额定容量的供电器可供放大器的最大级数,算式是很复杂的,而用VisaulFOXPRO6.0编写一个小程序,利用电脑对上述问题进行处理,就变得简单易用。 相似文献
42.
43.
Yu-Li Hsueh Jaedon Kim Ching-Fong Su Rabbat R. Hamada T. Tian C. Kazovsky L.G. 《Lightwave Technology, Journal of》2006,24(1):44-53
A sublambda traffic-grooming scheme on wavelength-division-multiplexed (WDM) rings, which is called optical burst transport (OBT), is proposed. The network protocol and architecture allow increased flexibility to tailor the transport network behavior for efficient delivery of bursty data traffic. Using different network parameters, its performance is analyzed via simulation, and the implementation issues including the media-access-control (MAC) protocol, tunable-filter controller, and burst-mode receiver are addressed. Finally, the feasibility of the OBT with an experimental testbed built by the authors is demonstrated and a streaming-video application is used to present its overall functionality. 相似文献
44.
45.
Triterpenoid Constituents of Huperzia miyoshiana 总被引:1,自引:0,他引:1
Thirteen triterpenoids, including three new ones, miyoshianois A (1), B (2) and C (3), were isolated from Huperzia miyoshiana. The structures of these new compounds were established as 3-O-dihydroferuloyltohogenol (1), 16-oxo-3β,21β-dihydrox-y-serrat-14-en-24-ferulate (2) and 16-oxo-3a, 21β-dihydroxy-serrat-14-en-24-ferulate (3), respectively, on the basis of their spectroscopic analysis. 相似文献
46.
We study a GI/M/c type queueing system with vacations in which all servers take vacations together when the system becomes empty. These servers keep taking synchronous vacations until they find waiting customers in the system at a vacation completion instant.The vacation time is a phase-type (PH) distributed random variable. Using embedded Markov chain modeling and the matrix geometric solution methods, we obtain explicit expressions for the stationary probability distributions of the queue length at arrivals and the waiting time. To compare the vacation model with the classical GI/M/c queue without vacations, we prove conditional stochastic decomposition properties for the queue length and the waiting time when all servers are busy. Our model is a generalization of several previous studies. 相似文献
47.
A fourth‐order compact finite difference scheme on the nine‐point 2D stencil is formulated for solving the steady‐state Navier–Stokes/Boussinesq equations for two‐dimensional, incompressible fluid flow and heat transfer using the stream function–vorticity formulation. The main feature of the new fourth‐order compact scheme is that it allows point‐successive overrelaxation (SOR) or point‐successive underrelaxation iteration for all Rayleigh numbers Ra of physical interest and all Prandtl numbers Pr attempted. Numerical solutions are obtained for the model problem of natural convection in a square cavity with benchmark solutions and compared with some of the accurate results available in the literature. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
48.
Yanqing Tian Xiaohe Xu Yingying Zhao Xinyi Tang Fengyu Su Xiaoguang Zhao Enle Zhou 《Liquid crystals》1995,19(3):295-300
The synthesis of three new series of chiral Schiff's bases containing benzilideneaniline and 2-hydroxybenzilideneaniline moieties as mesogenic cores is presented. Differential scanning calorimetry, optical polarizing microscopy and X-ray diffraction measurements were used to study the phase transition temperatures and behaviour. The results reveal that most of these materials show chiral smectic mesomorphism. 相似文献
49.
光照与彩陶俑表面色变关系的实验研究 总被引:1,自引:0,他引:1
本文以秦彩俑表面色彩为研究对象,通过光照实验与色彩变化的色度测量,分析了光照引起彩俑颜料色变的规律,为秦彩俑这一大型重点文物的色彩保护提供了科学理论依据. 相似文献
50.
金属迁移能导致混合微电路发生灾难性失效。本文介绍一种简单易行的测试方法-水滴试验法,来测量厚膜电路的实际金属迁移率。用引方法测量时,发现Pd-Ag导体的迁移率最大,Pt-Au导体的金属迁移率最小。 相似文献